A systematic and integrated investigation of hepatic protein metabolism in the rat will be conducted using the whole animal, the perfused liver and isolated hepatocytes and experimental models. The effects of fasting and selective refeeding will be studied to define the nature of the nutritional regulation of albumin and liver protein turnover. Hormone deprivation, supplementation, and interactions will be examined in the case of growth hormone, insulin, thyroxine, and glucocorticoids. An integrated approach will be carried out at the molecular level to quantitate the role of: amino acid transport and substrate availability; the size, distribution and quantity of total, membrane-bound, and free liver polysomes; the quantity and distribution of total free ribosome monomers and subunits; rates of peptide initiation and elongation; ribonuclease activity; total liver mRNA levels; and the quantitation of specific albumin-synthesizing polysomes and mRNA. Changes in these parameters will be used to localize sites of regulation of protein and albumin synthesis. Rates of protein degradation will also be examined. An emphasis will be placed on how the nutritional and hormonal environment of the liver cell controls protein metabolism and thereby regulates liver function.